Add DSCP support for POSIX platforms.

This CL only includes the necessary changes in PhysicalSocketServer,
and doesn't include the Java or Objective C API.

Note that this is doing exactly the same thing as UDPSocketPosix
in chromium.

BUG=webrtc:5658

Change-Id: I295455eaccba2a83cdd1bc55848f325c310f8d32
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168260
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Commit-Queue: Taylor <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30478}
diff --git a/rtc_base/physical_socket_server.h b/rtc_base/physical_socket_server.h
index e85b2b0..a71810f 100644
--- a/rtc_base/physical_socket_server.h
+++ b/rtc_base/physical_socket_server.h
@@ -199,11 +199,12 @@
   virtual void EnableEvents(uint8_t events);
   virtual void DisableEvents(uint8_t events);
 
-  static int TranslateOption(Option opt, int* slevel, int* sopt);
+  int TranslateOption(Option opt, int* slevel, int* sopt);
 
   PhysicalSocketServer* ss_;
   SOCKET s_;
   bool udp_;
+  int family_ = 0;
   CriticalSection crit_;
   int error_ RTC_GUARDED_BY(crit_);
   ConnState state_;